This invention relates to a fuel control system for a multiple cylinder engine and more particularly to an improved feedback control system for such engines.
It has been acknowledged that feedback control systems are very effective in controlling not only the fuel economy but also the exhaust emission of internal combustion engines. One type of control that operates on a feedback principle employs an exhaust combustion sensor in the exhaust system for sensing the air/fuel ratio. The air/fuel ratio is then adjusted in response to the output of this sensor so as to maintain the desired fuel/air ratio.
Such systems, although capable of use with four-cycle engines, do present certain problems when utilized with two-cycle engines. The reason for this is that two-cycle engines frequently employ a large degree of scavenging and hence the exhaust gases may not be truly representative of the combustion characteristics at the completion of the combustion cycle. That is, the combustion products may be diluted with a fresh charge and hence feedback control is difficult.
There has, therefore, been proposed a system wherein a sensor is positioned and related to a single cylinder of a multiple cylinder engine and which senses the combustion products in that cylinder only at the time when combustion has been substantially completed and before any significant scavenging has occurred. These systems are very effective.
However, if only a single sensor is employed for controlling all cylinders, then the cylinder-to-cylinder variations can be significant. For example, in outboard motors it is the common practice to employ an exhaust manifold that collects all of the exhaust gases from all of the cylinders and which discharges it to the atmosphere. Because of the fact that the exhaust-pipe exit is spaced at different distances from the individual exhaust ports and because of the pulse-back effect, there can be wide cylinder-to-cylinder variations. In addition, the variations between cylinders is not the same under various running conditions.
This problem can be accommodated by providing an independent sensor for each cylinder of the engine. That obviously provides a very complicated and expensive solution to the problem.
It is, therefore, a principle object of this invention to provide an improved feedback control system for a multiple cylinder engine wherein one sensor is employed for controlling all cylinders.
It is a further object of this invention to provide a single sensor feedback control system for an engine wherein cylinder-to-cylinder variations are automatically accommodated for.